In a wireless communication system, a transmission direction from a base station to a mobile station (terminal) is defined as a downlink and a transmission direction from the terminal to the base station is defined as an uplink.
In general, in the wireless communication system, the base station calculates a round trip time (RTT) from an initial access signal that is transmitted from the terminal. When the base station informs the terminal about the calculated RTT, the terminal transmits a signal as early as the RTT whereby the base station and the terminal maintain uplink synchronization. The above method is used in a portable telephone system or a wireless local area network (WLAN) system.
However, the above method is not suitable for a marine wireless communication system. In the case of land wireless communication, generally, the terminal periodically transmits information and a propagation delay time is also very short as compared to marine wireless communication. At sea, the propagation delay time is very long and communication does not occur as frequently as on land. Through marine wireless communication, e-mail or information such as a marine map, weather data, travel route data of a ship and the like are transmitted and received. When providing the above communication service, there is no need to continuously maintain uplink synchronization. Only, there is a need to provide an appropriate service opportunely in response to a service request that occurs from time to time.
Further, in the marine wireless communication, it is difficult to use a wide bandwidth as used in the land wireless communication. Accordingly, it is necessary to efficiently use an allocated bandwidth and a further simpler communication scheme is required.